Protection device, corresponding method and computer software product

ABSTRACT

A device is provided for protecting an electronic payment terminal, which includes at least one printed circuit and one casing. The device includes at least one capacitive detector having a first part electrically connected to the printed circuit and a second part mounted within the casing of the electronic payment terminal without being electrically connected to the first part. The at least one capacitive detector is configured to deliver a reference capacitance when it is mounted in the electronic payment terminal. The device also includes a capacitive measurement microprocessor electrically connected to the at least one capacitive detector and configured to detect a variation in capacitance of the at least one capacitive detector. The device includes a transmitter for transmitting a piece of information representing the variation in capacitance when an absolute value of a difference between the measured capacitance and the reference capacitance exceeds a predetermined threshold.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

THE NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

None.

FIELD OF THE DISCLOSURE

The present disclosure pertains to the field of the securing of paymentdevices.

The present disclosure pertains more particularly to a device enablingthe detection of an intrusion into an electronic payment terminal or anopening of this terminal aimed at fraudulently obtaining confidentialdata such as bank data.

There are many devices enabling users to pay for purchases. Moreparticularly, payment devices using bank cards such as smart chip cardsor smart magnetic stripe cards have become widespread. These devices aregenerally called payment terminals and enable simple and quick paymentfor purchases. There are other devices too using smart chip or magneticstripe cards: these are for example bank terminals such as automatedteller machines or automated cash dispensers. Here below, all thesedevices, which include both an entry keypad and a memory card reader arecalled payment terminals.

Owing to the data handled, payment terminals attract the attentions offraudulent individuals. These individuals use every possible means totry and access the confidential data that are exchanged in theterminals.

One of the ways of accessing these pieces of data consists is tointroduce a bug into the terminal. This bug is used to retrieve dataexchanged between the terminal and the bank card to make a copy of thisconfidential data with the aim of forging false payment cards.

BACKGROUND OF THE DISCLOSURE

All payment terminal providers and a certain number of third-partyproviders are capable of providing anti-intrusion solutions of varyingdegrees of efficiency.

Indeed, the fraudulent individuals constantly increase their ingenuitywhen trying to circumvent such and such a protection measure.

For obvious reasons of security, the opening of an electronic paymentterminal or the intrusion of a foreign element into an electronicpayment terminal or again the assembling of a terminal are impermissibleoperations.

Anti-intrusion measures being proposed include the application of falsekeys which are used to detect the opening of the terminal. When theterminal is mounted, the keypad of the terminal exerts pressure on thefalse keys which are therefore in permanent contact with the printedcircuit. When the keypad is removed, the false keys are no longer incontact with the printed circuit and the security processor activatesthe requisite protection measures. One of the problems with these falsekeys is related to the fact that additional mechanical parts need to beprovided on the keypad support to detect the dismantling of the keypad.These additional mechanical parts are costly.

We may also cite the use of lattices for protecting printed circuits toprevent the insertion of probes. A probe generally takes the form of analmost invisible thin metal wire that is inserted into the electronicpayment terminal through the bank card insertion slot to access thecontacts between the bank card and the card reader (these contacts arealso called “pins”).

There are many other existing measures. However, these measures are notalways efficient.

One protective solution that can be envisaged is that of preventing there-assembly of a terminal from parts belonging to other terminals. Thissolution comes into play when fraudulent individuals try to fabricate orreassemble a terminal. This is a problem complementary to that ofintrusion.

To date, there is no approach by which this problem can be resolved fora cost deemed to be reasonable. Indeed, it is theoretically possible toprovide the components of the terminal with identification. To this end,each component must be provided with an identifier, for example an RFID,and a security processor installed in the terminal has to be providedwith the list of the identifiers of the In addition to being complexthis operation also costly since the RFID tags used to identify thecomponents considerably increase the cost of the terminal. Now, it isimportant to provide payment terminals that users can trust and that arenot excessively costly to produce.

SUMMARY

An exemplary embodiment of the invention does not have the drawbacks ofthe prior art.

An exemplary embodiment of the invention pertains to a device forprotecting an electronic payment terminal comprising at least oneprinted circuit and one casing, the device for protecting beingcharacterized in that it comprises:

-   -   at least one capacitive detector comprising two parts, a first        part electrically connected to said printed circuit and a second        part mounted within said casing of said electronic payment        terminal without being electrically connected to said first        part, said at least one capacitive detector being configured to        deliver a reference capacitance when it is mounted in said        electronic payment terminal;    -   a capacitive measurement microprocessor electrically connected        to said at least one capacitive detector, configured to detect a        variation in capacitance of said at least one capacitive        detector;    -   means for transmitting a piece of information representing said        variation of capacitance when an absolute value of a difference        between said measured capacitance and said reference capacitance        exceeds a predetermined threshold.

Thus, an exemplary embodiment of the invention makes it possible tosense an attempted intrusion or dismantling of the electronic paymentterminal. Indeed, any such attempt against a portion of the terminalprotected by the device of an exemplary embodiment of the inventionprompts a variation in the measured capacitance beyond a predefinedvalue and leads to the transmission of information on this variation tothe security microprocessor of the terminal which takes the necessarymeasures (for example the erasure of the secured memory).

An exemplary embodiment of the invention thus improves the security ofthe electronic payment terminal and more particularly participates in anactive securing of the terminal.

According to one particular embodiment, said device for protectingfurther comprises calibration means delivering said referencecapacitance.

According to one particular embodiment, said capacitive detector furthercomprises a third part consisting of at least one polyhedral elementlined with a conductive surface.

According to one particular characteristic, said at least one third partis positioned on said casing of said terminal.

According to one particular characteristic, said at least one third partdefines a unique capacitance associated with said casing of saidterminal.

According to another aspect, an exemplary embodiment of the inventionalso pertains to a method for protecting an electronic payment terminalcomprising at least one printed circuit and one casing, said device forprotecting comprising:

-   -   at least one capacitive detector comprising two parts, a first        part electrically connected to said printed circuit and a second        part mounted within said casing of said electronic payment        terminal without being electrically connected to said first        part, said at least one capacitive detector being configured to        deliver a reference capacitance when it is mounted in said        electronic payment terminal;    -   a capacitive measurement microprocessor electrically connected        to said at least one capacitive detector, configured to detect a        variation in capacitance of said at least one capacitive        detector;    -   means for transmitting a piece of information representing said        variation of capacitance when an absolute value of a difference        between said measured capacitance and said reference capacitance        exceeds a predetermined threshold.        According to an exemplary embodiment of the invention, said        method for protecting comprises at least one iteration of the        following steps:    -   measuring a current value of capacitance by means of said        capacitive detector;    -   computing said absolute value of a difference between said        measured capacitance and said reference capacitance;    -   transmitting said piece of information representing said        variation of capacitance when said absolute value exceeds said        predetermined threshold

According to an exemplary embodiment of the invention, said method forprotecting comprises, during a first powering on of said electronicpayment terminal, a step for calibrating said terminal delivering saidreference capacitance.

An exemplary embodiment of the invention thus improves the security ofthe electronic payment terminal and more particularly takes part in anactive securing of the terminal.

According to another aspect, an exemplary embodiment of the inventionpertains to a computer software product downloadable from acommunications network and/or stored on a computer-readable carrierand/or executable by a microprocessor. According to an exemplaryembodiment of the invention, such a computer software program comprisesprogram code instructions to execute the protection method as describedhere above when it is executed on a microprocessor.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages shall appear more clearly from thefollowing description of an embodiment, given by way of a simpleillustratory and non-exhaustive example and from the appended drawings,of which:

FIG. 1 is a drawing of a detection device according to an embodiment ofthe invention applied to a false key;

FIGS. 2 and 3 illustrate an embodiment of the invention in which thedetection device comprises a two-part capacitive detector;

FIG. 4 illustrates an embodiment of the invention in which the detectiondevice comprises a three-part capacitive detector;

FIG. 5 is a schematic view of a payment terminal according to anembodiment of the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 1. Description of anEmbodiment

The principle of an exemplary embodiment of the invention provides theelectronic payment terminal with an ability to monitor its internalcapacitive environment and implement security measures based on themeasurement of capacitances.

Implementing such measures is simpler than implementing a multiplicityof protection devices and methods, generally based both on a mechanicalcomponent and on an electronic component. On the contrary, themeasurement of capacitance by the electronic payment terminal, at theunits to be protected, is simple and requires only the installation of aconductive element such as for example an electrical wire or aconductive paint.

In one embodiment, the invention also enables the implementing of ahardware identification of the terminal that is simple and costs little.An exemplary embodiment of the invention also makes it possible tomanage anti-intrusion devices simply and at low cost. An exemplaryembodiment of the invention relies on a capacitive measurement madebetween one or more capacitive detectors which are formed by at leasttwo parts. Thus, unlike in classic capacitive detectors enabling adetection of a variation in capacitance, for example when an object isbrought close to a detector, an exemplary embodiment of the inventionproposes capacitive detectors made up of several parts.

An exemplary embodiment of the invention thus proposes the detecting ofa modification of the capacitance (i.e. a modification of the electricalcharge) of the detector when one of the parts of the detector is shiftedor modified relatively to the other part of the detector.

To this end, the device according to an exemplary embodiment of theinvention comprises at least one capacitive detector comprising twoparts, a first part electrically connected to said printed circuit and asecond part mounted within said casing, said at least one capacitivedetector being configured to deliver a reference capacitance. Thiscapacitive detector includes a preliminarily determined capacitanceknown to a capacitive measurement microprocessor, electrically connectedto the capacitive measurement support and configured to detect avariation in capacitance of the capacitive measurement support. Thedevice also comprises a transmitter configured for transmitting a pieceof information representing variation in capacitance when an absolutevalue of a difference between a measured capacitance at a given instantand the reference capacitance exceeds an also predetermined threshold.

Here below, we present exemplary embodiments. These embodiments can ofcourse be combined within one and the same terminal in order thatseveral security measures may be available.

2. False Keys

As mentioned preliminarily, the joining on of false keys enablesdetection of the dismantling of the keypad. The false keys are used toset up a permanent connection, by pressure, between the keypad and theprinted circuit. Usually, the false keys set up an electrical connectionthat is monitored to detect opening. This system is relatively complexto implement. On the contrary, implementing false keys by means of atwo-part capacitive detector does not require any complex implementationas already described with reference to FIG. 1.

A false key according to an exemplary embodiment of the invention takesthe form of a metal “convex spring-operated dome” 13″, constituting asecond part of the two-part capacitive detector 13. This dome 13″ ismounted on the printed circuit 10 which is positioned in the terminal. Aground plane 12 is drawn on the printed circuit 10. The first part 13′of the “capacitive detector” 13 is positioned beneath the dome 13″,between the conductive parts of the ground plane. The first part 13′ ofthe “capacitive detector” 13 is not electrically connected to the groundplane but electrically connected to the capacitive microprocessor (notshown). The first part 13′ of the “capacitive detector” 13 and theground plane 12 are buried beneath a layer 14 of prepreg+FR-4 varnishalone well known to those skilled in the art.

The keypad 15 for its part is provided with a push button 15-1. Duringassembly, this push button 15-1 crushes the dome 13″. The referencecapacitance is then recorded during the first powering on of theelectronic payment terminal. This reference capacitance corresponds tothat of the terminal when it is assembled.

If the keyboard of the terminal is dismantled, the dome 13′ resumes itsinitial shape leading to a modification of the capacitance and thereforea detection of the opening. Thus, according to an exemplary embodimentof the invention, it is not necessary to provide for an electricalconnection of the dome 13′ with the printed circuit 10, and this greatlysimplifies the implementation.

3. Division of the “Capacitive Detector” into Two Parts

Referring to FIGS. 2 and 3, a description is provided of an embodimentof the invention in which the “capacitive detector” is formed by twoparts.

In this embodiment of the invention, a first part 13′ of the “capacitivedetector” 13 is directly integrated into the printed circuit 10 as atrack of this printed circuit. In one alternative embodiment (FIG. 3),the first part of the capacitive detector 13 is shifted to a support13-1, which is itself bonded to the integrated electronic circuit 10 towhich the first part 13′ of the capacitive detector 13 is electricallyconnected (13-2).

A conductive surface, which constitutes the second part 13″ of thecapacitive detector 13 is positioned on the casing 16 of the terminal.When the terminal is closed, this second part 13″ is positioned againstthe first part 13′ of the “capacitive detector” 13.

The first part 13′ and the second part 13″ of the capacitive detector 13can be coated with an insulator material or directly poured into theplastic, and do not need to be in direct contact, i.e. it is notnecessary that the first part 13′ and second part 13″, which areconductive parts, of the “capacitive detector” 13 should be in contact.It is also possible to consider leaving a space between the two.

Should the terminal be open, the value of the capacitance measured bythe “capacitive detector” 13 is greatly modified relatively to thereference value, and the opening of the terminal is detected. Theappropriate security measures are then implemented (erasure of thememory of the terminal or only erasure of the secured memory).

The parts of the “capacitive detector” consist of a conductive surface.A single wire is enough to make these connected surfaces.

4. Anti-Intrusion in a Volume with Single Identification Scheme

In this embodiment of the invention presented with reference to FIG. 4,aimed firstly at preventing the opening of the electronic paymentterminal and secondly at making any attempt at snooping by conventionalsnooping means very improbable, the capacitive detector 13 is alsoformed by several parts (13′, 13″ and 13′″).

As in the previous embodiment, the first part 13′ of the “capacitivedetector” 13 is directly integrated into the printed circuit 10 as atrack of this printed circuit (or shifted to a support) as indicated inFIGS. 2 and 3.

The base of the casing 16 is lined with a conductive paint (or surface)connected to ground. This conductive surface which extends to the bottomof the casing is the second part of the capacitive detector. The factthat this second part 13″ of the “capacitive detector” is connected toground offers major advantages.

Through the Faraday cage effect, the volume defined by the conductivepaint or conductive surface is insulated from external electromagneticdisturbances. Moreover, the variations in measurements of capacitance ofthe capacitive detector are easy to identify.

This system also greatly reduces the possibilities of electromagneticsnooping on confidential data (PIN, etc). The volume under surveillanceis therefore clearly demarcated and determined by the ground planes.

Polyhedral elements with conductive surfaces are also laid out in thecasing. These polyhedral elements are the third part 13″′ of thecapacitive detector 13. These polyhedral elements (13″′-1 to 13″′-4) canbe an integral part of the casing or permanently bonded to it. Thesepolyhedral elements are used to identify the casing so as to connect acasing to a single printed circuit. This technique is called“identification by volume pattern”.

Thus, in addition to their anti-intrusive function, the third part ofthe capacitive detector 13′″ fulfils a function of identifying thecasing and provides an additional level of security.

Indeed, the fact of modifying these polyhedral elements (for exampletheir shape) or their locations significantly modifies the field linesand therefore the value of the capacitance measured by the capacitiveprocessor. Thus, if an attempt is made to reassemble a terminal fromseveral components of other terminals, and especially from a new casing,the reassembled terminal will not be correctly identified.

To reassemble a complete terminal, an attacker cannot re-utilize any newcasing whatsoever; it would be necessary for him to use exactly the samecombination of polyhedral elements and, for this purpose, he must knowthis combination. It is easy for the terminal manufacturer to vary theshape, thickness, location so as to obtain a large number of possiblecombinations and therefore almost nullify the probability that theattacker might recreate the initial capacitive environment of theelectronic payment terminal. Thus, even if the attacker successfullyreassembles a terminal, it will be unusable.

However, these polyhedral elements are not indispensable to theanti-intrusion function as such. The additional polyhedral elements areused to make the terminal unique at a marginal cost as compared with thecost of joining on of RFID tag chips.

An opening or an intrusion by a very small object that is partlyconductive (or even by a dielectric component under certain conditions)is detected and identified as a “attack” leading to the terminal beingplaced “attack” mode (and leading to an erasure of the confidential datathat it contains).

The capacitive detector may consist of a single conductive track, asingle wire being enough. It may also be lined with a plastic film orcast in the plastic support of the shell of the terminal.

The last-named technique can apply to the complete terminal or tospecific volumes of the terminal.

Another advantage of this technique based on a three-part capacitivedetector is that it very sharply limits electromagnetic emissions fromthe electronic system of the electronic payment terminal making anysnooping on confidential data very improbable and also overcomeselectromagnetic environmental disturbances through a ground plane system(using the Faraday cage principle).

Furthermore, this system, in parallel with the environmentalcompensation system (see here below), provides efficient protectionagainst untimely and unsuitable detection of “attacks” due to changesoccurring in the surroundings (for example the reception of a call by acell phone placed beside the terminal etc) causing the loss of secretkeys of the terminal. Indeed, these losses of keys entail a majormaintenance costs which must be avoided, especially when the paymentterminal is the only terminal installed in a sales point.

5. Initial Parametrizing

To make it possible to provide the expected service, the device of anexemplary embodiment of the invention is parameterized in order todetermine the predetermined value of the reference capacitance. Asalready explained, this reference capacitance makes it possible tocontrol the variation of capacitance over time and determine whetherthis variation exceeds a predetermined value.

When the electronic payment terminal within which the device of anexemplary embodiment of the invention is mounted is first powered on, ameasurement of calibration and a parameterization are performed in orderto identify the reference value at rest in a neutral electromagneticenvironment of the capacitance of the capacitive detector.

Subsequently, this initial calibration sets up the referencecapacitance. In standard operating mode, a variation of the capacitancemeasured relatively to the reference capacitance is of course accepted,to enable normal working of the electronic payment terminal.

A value known as “delta” sets the upper and lower bounds within whichthe measured capacitances will be considered to be valid. Themeasurements are made periodically, either at regular intervals or atpredefined times (at night for example).

In the event of a cut in the mains electrical power supply, the securityunits of the terminal continue to work on battery. In this case, asystem for periodically putting the capacitive processor to sleep orreviving it enables regular measurement of the capacitive detectors (forexample every 500 milliseconds).

Indeed, since the device of an exemplary embodiment of the inventionconsumes very little electrical current, it can be implemented withoutany mains electrical power supply. Thus, the system of an exemplaryembodiment of the invention can provide for the security of the terminalcontinuously with or without the presence of mains current.

Under certain conditions, a system of compensation for ambientconditions can modify the reference value or base line. Such a systemcan be joined on to the device of an exemplary embodiment of theinvention to provide for efficient operation of the electronic paymentterminal as a function of the surroundings in which it is installed.

A software filtering is also performed to highlight events modifyingfield lines that are not true operations of installing fraudulentdevices (handling of the terminal etc).

All these measurements are driven by a micro-program associated with thecapacitive measurement microprocessor.

Referring to FIG. 5, we present an embodiment of a payment terminalaccording to an exemplary embodiment of the invention.

Such a terminal comprises a memory 51 constituted by a buffer memory, aprocessing unit 52, equipped for example with a microprocessor P, anddriven by the computer program 53 implementing the protection methodaccording to an exemplary embodiment of the invention.

At initialization, the instructions of the computer program code 53 arefor example loaded into a RAM and then executed by the processor of theprocessing unit 52. The processing unit 52 inputs at least one piece ofinformation I such as identifiers of localization areas. Themicroprocessor of the processing unit 52 implements the steps of theprotection method described here above according to the instructions ofthe computer program 53 to deliver a piece of processed information Tsuch as the detection of an attack leading to the elimination of theprotected data. To this end, the terminal comprises, in addition to thebuffer memory 51:

-   -   at least one capacitive detector comprising two parts, a first        part electrically connected to said printed circuit and a second        part mounted within said casing of said electronic payment        terminal without being electrically connected to said first        part, said at least one capacitive detector being configured to        deliver a reference capacitance when it is mounted in said        electronic payment terminal;    -   a capacitive measurement microprocessor electrically connected        to said at least one capacitive detector, configured to detect a        variation in capacitance of said at least one capacitive        detector;    -   a transmitter configured for transmitting a piece of information        representing said variation of capacitance when an absolute        value of a difference between said measured capacitance and said        reference capacitance exceeds a predetermined threshold.

These elements are driven by the microprocessor of the processing unit.

Although the present disclosure has been described with reference to oneor more examples, workers skilled in the art will recognize that changesmay be made in form and detail without departing from the scope of thedisclosure and/or the appended claims.

The invention claimed is:
 1. A device for protecting an electronicpayment terminal, said electronic payment terminal comprising at leastone printed circuit and one casing, wherein said device for protectingcomprises: at least one capacitive detector comprising a first partelectrically connected to said printed circuit, a second part mountedwithin said casing of said electronic payment terminal without beingelectrically connected to said first part, and a third part comprisingat least one polyhedral element lined with a conductive surface, said atleast one capacitive detector being configured to deliver a referencecapacitance when said at least one capacitive detector is mounted insaid electronic payment terminal, wherein said at least one polyhedralelement has at least one of a shape, thickness or location that isunique for said device, and wherein the second part changes at least oneof shape or location relative to the first part when the terminal isdismantled leading to a variation in a measured capacitance; acapacitive measurement microprocessor electrically connected to said atleast one capacitive detector, configured to detect a variation incapacitance of said at least one capacitive detector; a transmitter fortransmitting a piece of information representing said variation incapacitance when an absolute value of a difference between said measuredcapacitance and said reference capacitance exceeds a predeterminedthreshold.
 2. The device for protecting according to claim 1, whereinthe device further comprises a calibrator configured to deliver saidreference capacitance.
 3. The device for protecting according to claim1, wherein said at least one third part is positioned on said casing ofsaid terminal.
 4. The device according to claim 1, wherein said at leastone third part defines a unique capacitance associated with said casingof said terminal.
 5. The device of claim 1, wherein the second part ofthe capacitive detector comprises a conductive surface that lines abottom of the casing so as to define a volume of space within the casingthat is insulated from external electro-magnetic disturbance.
 6. Amethod for protecting an electronic payment terminal, comprising atleast one printed circuit and one casing, said method comprising atleast one iteration of the following steps: measuring a current value ofcapacitance by at least one capacitive detector of a device comprising:said at least one capacitive detector, which comprises a first partelectrically connected to said printed circuit, a second part mountedwithin said casing of said electronic payment terminal without beingelectrically connected to said first part, and a third part comprisingat least one polyhedral element lined with a conductive surface, said atleast one capacitive detector being configured to deliver a referencecapacitance when said at least one capacitive detector is mounted insaid electronic payment terminal, wherein said at least one polyhedralelement has at least one of a shape, thickness or location that isunique for said device, and wherein the second part changes at least oneof shape or location relative to the first part when the terminal isdismantled leading to a variation in a measured capacitance; and acapacitive measurement microprocessor electrically connected to said atleast one capacitive detector, configured to detect a variation incapacitance of said at least one capacitive detector; computing anabsolute value of a difference between said measured capacitance andsaid reference capacitance; and transmitting a piece of informationrepresenting said variation of capacitance when said absolute valueexceeds said predetermined threshold.
 7. The method according to claim 6wherein the method further comprises, during a first powering on of saidelectronic payment terminal, a step of calibrating said terminaldelivering said reference capacitance.
 8. An electronic payment terminalcomprising: at least one printed circuit and one casing; at least onedevice for protecting the electronic payment terminal, the devicecomprising: at least one capacitive detector comprising a first partelectrically connected to said printed circuit, a second part mountedwithin said casing of said electronic payment terminal without beingelectrically connected to said first part, a third part comprising atleast one polyhedral element lined with a conductive surface, said atleast one capacitive detector being configured to deliver a referencecapacitance when said at least one capacitive detector is mounted insaid electronic payment terminal, wherein said at least one polyhedralelement has at least is unique for said device, and wherein the secondpart changes at least one of shape or location relative to the firstpart when the terminal is dismantled leading to a variation in ameasured capacitance; a capacitive measurement microprocessorelectrically connected to said at least one capacitive detector,configured to detect a variation in capacitance of said at least onecapacitive detector; a transmitter, which transmits a piece ofinformation representing said variation in capacitance when an absolutevalue of a difference between said measured capacitance and saidreference capacitance exceeds a predetermined threshold.
 9. Anon-transitory computer-readable carrier comprising a computer softwareproduct stored thereon and executable by a microprocessor, the productcomprising program code instructions to execute a method for protectingan electronic payment terminal when the program is executed on amicroprocessor, wherein the method comprises at least one iteration ofthe following steps: measuring a current value of capacitance by atleast one capacitive detector of a device comprising: said at least onecapacitive detector, which comprises a first part electrically connectedto a printed circuit, a second part mounted within a casing of saidelectronic payment terminal without being electrically connected to saidfirst part, and a third part comprising at least one polyhedral elementlined with a conductive surface, said at least one capacitive detectorbeing configured to deliver a reference capacitance when said at leastone capacitive detector is mounted in said electronic payment terminal,wherein said at least one polyhedral element has at least one of ashape, thickness or location that is unique for said device, and whereinthe second part changes at least one of shape or location relative tothe first part when the terminal is dismantled leading to a variation ina measured capacitance; and a capacitive measurement microprocessorelectrically connected to said at least one capacitive detector,configured to detected a variation in capacitance of said at least onecapacitive detector; computing an absolute value of a difference betweensaid measured capacitance and said reference capacitance; andtransmitting a piece of information representing said variation ofcapacitance when said absolute value exceeds said predeterminedthreshold.